Question: 3 markers cost $4.41. Which equation would help determine the cost of 4 markers?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 4 markers. Since 4 markers cost $x$ , we have the following proportion: $\dfrac{4}{x}$ We can write the fact that 3 markers cost $4.41 as a proportion: $\dfrac{3}{\$4.41}$ The cost changes along with the number of markers purchased, and so the two proportions are equivalent. $\dfrac{4}{x} = \dfrac{3}{\$4.41}$